horton



Oct. 16, 1934. J. w. HORTON SYNGHRONIZING SYSTEM- 2 Sheets-Sheet 1 Filed Dec. 27, 1930 INVENTOR J. W-HORTON A TTORNE Y Oct. 16; 1934. .1. w. HORTON SYNCHRONIZING SYSTEM Filed Dec. 27. 1930 2 sheets-sheet 2 A TTORNEV lit Patented Oct. 16, 1934 PATENT OFFICE increase I sirncm omzme srs'rnm .lloseph W. lhlorton, Cambridge, Mass... assignor to Bell Telephone Laboratories, Incorporated, New York, N. K, a corporation oi New York mplication December 27, rest, hcrial No. 565,620

This invention relates to synchronizing systems and more particularly to methods of and systems for indicating whether remotely placed rotating members are in synchronism and in phase with 7 each other. r

The prior art includes a disclosure of a system for stroboscopically indicating that two remotely placed rotating members are in synchronism and in phase with each other. in this system a limited angular sector of a rotating cylinder is provided with a number of black lines to form a screen which interrupts the light reflected from it to a photo-electric cell to cause the production of a succession of current impulses. These impulses are applied to a Kerr cell to control a beam of light which illuminates a sector or a transparent disc, corresponding in angular extent to the lined sector of the cylinder, provided with black lines equal in number to those on the cylinder. lhe disc is geared to a second cylinder, whereby these elements are rotated at the same speed, and the two cylinders are intended to be operated in synchronism and in phase with each other.

Provided the lined sector on the disc passes through the light beam at the instant the intensity of the latter is being varied by the current impulses, the varying light and the lines on the disc co-operate stroboscopically to produce a pattern consisting of a plurality of lines. This pattern appears to stand still if the first cylinder and the disc, and hence the second cylinder, are in synchronism with each other. Otherwise the pattern appears to move in one direction or the other.

The varying light beam, supplied by the receiving source, can only illuminate the lined sector on the disc when the two cylinders are substantially in synchronism and in phase with each other. To effect phase adjustment, the driving connection for the second cylinder and disc is provided'with a slip coupling, which may be actuated to adjust them relatively to the drive shaft and hence-the phase of the second cylinder with respectto'the first cylinder. One disadvantage of the system just described is that it utilizes only a few per cent of thetotal illumination for proclucing a pattern consisting of a plurality of closely adjacent lines which differ but slightly in tone values from each other and hence which do not stand out sharply so as to be distinguished from each other. Another disadvantage resides in the fact that the pattern is only visible when the two cylinders are approximately in synchronism and in phase with each other.

'the present invention provides a system of the type described above which does not embody the disadvantages noted above.

An object of the invention is to utilize the available illumination most advantageously.

Another object is to produce a single reference line in a field'which difiers sharply in tone value therefrom.

Still another object is to produce an image having a reference line the position of which is a positive indication of the phase relation of the discs.

An additional object is to produce a pattern including a reference line which is visible when the two moving members approach synchronism, whether they are in phase with each other or not.

In one embodiment of the invention, illustrating its use in picture transmission systems, the rotating cylinder at the transmitter is provided at one end with a peripheral band made up of black and white sections. A beam of light is projected through a fixed aperture upon the band and the white sections reflect light to a photo-electric cell to cause current impulses to be transmitted to a light source supplying a beam of light for intermittently illuminating the entire surface of a receiving band, similar to that at the transmitter, which rotates at the same speed as the cylinder carrying the picture recording film.

The bands are half black and half white, and the sections are so arranged, relatively to one another and as to their relative lengths, that the light, reflected from the receiving band plotted in terms of the per cent of light reflected from a white section continuously illuminated, is substantially uniform with two relatively high intensity peaks separated by zero illumination once per revolutionof the band as the rotating cylinders approach synchronism. In this arrangement the light applied to the receiving band has an apparent intensity equal to fifty per cent of the total available light. Since the receiving band is half white and half black, the apparent average intensity of the illumination applied toll; is equal to twenty-five per cent of that of a white band continuously illuminated by the total available light. Due to the timing of the light interruptions and sequence of the black and white areas of the receiving band, there appears, as synchronism is approached, a black line in a field which appears whiter immediately adjacent the line than at other portions of the field. This black line appears to move in one direction or the other as synchronism is approached, but becomes stationary when the cylinders are in synchronism. i M

The position of the black line is a positive indication of the phase relation of the cylinders. Phase adjustment can be eflected by momentarily changing the speed of the receiving cylinder to cause the black line to occupy a predetermined position in the field.

A detail description of the invention follows and'is illustrated in the attached drawingain which:

Fig. 1 schematically illustrates a simple apparatus for practicing the invention;

Fig. 2 illustrates the discs included in Fig. 1 looking in the direction indicated by arrows a;

' Fig. 3 shows a curve which will be used to ex--' plain the operation of the apparatusof Fig. 1;

Fig. 4 is a diagrammatic showingof a picture transmission system involving the invention;

Figs. 5 and 8 show details of the apparatus of Fig. 4; and

Figs. 7 and 8 illustrate alternative arrangements which may be used in place of the receiving apparatus of Fig. 4.

As shown in Fig. '1, it is assumedthat the motors 1 and 2, each supplied with energy from a suitable source (not shown) are to be synchronized. Either motor maybe provided with a unit whereby its speed of rotation may be controlled, herein illustrated by way of example as applied to motor 2 and consisting of a rheostat 3.

Motor 1 drives an opaque disc 4 having a series of segmental openings 5 to 12, inclusive, the angular' lengths of which vary in a predetermined sequence, arranged in a circle near its periphery, and the motor 2 drives a white disc 13 upon which is provided a series of black sectors 14 to 22 inclusive the angular lengths of which vary in a predetermined sequence, arranged in a circle near its periphery.

The discs 4 and 13 are of the same diameter and, as shown in Fig. 2, the openings in disc 4 and the black sectors of disc 13 are the same distance from the centers ofand are arranged in the same order, as determined by their lengths, around the centers of the respective discs.

Light of constant intensity, supplied by a source 23, is gathered by a lens 24 and projected in the form of a beam, which passes through an aperture 100 in a mask 125, upon the portion of the disc 4 having the circle of openings 5 to 12. The peripheral length of aperture 100 should be equal to or less than the peripheral length of the shortest of the openings 5 to 12. As the disc 4 is rotated light passes through the aperture 100' and the successive openings 5 to 12 to illuminate,

the whole face of the disc 13 carrying the black sectors 14 to 22, which co-operate with the intervening white segments of the disc to constitute a black and-white circular band.

In one specific design, the complete band of disc 4 comprises an opening 5 of one unit length and a solid area of one unit length, an opening area of two unit lengths, an opening 12 of three unit lengths and a solid area of three unit lengths.

' Thus, the band comprises thirty-six unit lengths of which eighteen are openings and eighteen solid area, consequently fifty per cent of the total light supplied by source 23 is used during each revolution to illuminate the disc 13.

The sectors and intervening white sections of disc 13 are arranged in the same sequence as the openings and solid-areas of disc 4. The band on disc 13 consists of thirty-six unit lengths of which eighteen are white and'eighteen black. Hence 50 percent of the light supplied to this disc is reflected by the white sectors, or 25 percent of the light supplied by source 23.

Suppose that motor 1 is operating at the desired speed and that motor 2 is to be brought into synchronism with it. As the motor 2 comes up to speed the light supplied through the succession of openings 5 to 12 will illuminate all of the black and white sectors of disc 13 to produce a 'stroboscopic pattern, the-color of which is gray.

As the speed of the motor 2 approaches that of motor 1, the pattern will appear to rotate and to consist of a gray ring, one portion of which is considerably lighter in color than the remainder with a black line in the middle of the light colored section. when synchronism is attained, the pattern will be stationary and appear plotted in terms of the percentage of light which would be reflected from a white band continuously illuminated. The ordinates represent percentage and the abscissae represent positions along the stroboscopic image.

If the two discs are rotating there will be one point on the image such that black sectors only appear during the intervals of illumination hence no light will be reflected from this point which will behereinafter referred to as the point of zero illumination.

At positions displaced along the image from the point of zero illumination, by amounts corresponding to 1, 2 and 3 unit lengths during one revolution of the disc, there will be respectively 1 eight, twelve and ten white unit areas which coincide with intervals of illumination. As the displacement progresses to the thirty-second position the number of white unit areas per revolution which coincide with inmrvals of illumina- 1 tion-will vary between 10 and 7. At the thirtythird position there will be ten such unit areas, at the thirty-fourth position twelve areas, at the thirtysfifth position eight areas and at the thirtysixth, when the first position reoccurs, no white 1 unit areas are illuminated. At the second and thirty-fourth positions 33 percent of the total number of areas of the disc are reflecting light during intervals 'of illumination. Midway between these positions is the position at which no 1 white sectors of the disc appear during intervals of illumination and throughout the remainder of the positions the number of reflecting areas will vary between slightly less than 20 percent and about 27.5 percent. This will result in the production of an image the major portion of which is substantially uniform in tone value, but has two more brilliantly illuminated sections close to each other, which are separated by a nonilluminated section. When the speed of the two motors diifers, the image will appear to rotate in one direction or the other. If this difference in speed is great, the image will rotate too rapidly for the non-illuminated sector to be visible, but,

as the motors approach synchronism, the image 156 v image.

caused to occupy a position opposite the referv,ence mark with the pattern stationary. When this o'ccurs'the two motors will be in synchronism and in phase with each other. The speed of motor 2 may be regulated by adjusting the rheostat 3. 1

If the'light illuminates a single narrow sector of the receiving band, the curve of Fig. 3 indicates the variation of light reflected from the il-= luminated sector as the two bands go through a complete phase cycle.

The picture transmission system of Fig. a comprises a source 25 of constant light, a lens 26 for focusing the light from source 25 upon the picture 2'? carried by a drum 28, which is given. a motion of rotation and translation in accordance with standard practice, and a light sensitive device 129 which is actuated by light reflected from the picture to cause the production of image currents varying as the tone value of successive elemental areas of the picture. Drum28 is mounted to rotate freely ona shaft 29 supported by bearings carried by the standards 39 and 31 and is driven by a motor (not shown) through a coupling unit, which permits the charts to be brought up to the desired speed of rotation and, while rotatingat that speed, to be given a motion of translation.

The driving unit comprises a worm 32, carried by the shaft of the motor, which meshes with a gear 33 mounted in supports 42 and provided with a key 3% engaging in a keyway 35 provided in an extension 36 formed integral with or connected to the drum 28, whereby the latter may be rotated. Drum 28 is provided with a nut 37 which engages a screw thread on the shaft 29, and a support 45 provided with a surface 38 which contacts with a disc 39 secured to the shaft 29. Surface 38 and disc 39 constitute a friction clutch for mechanically connecting the shaft 29 to the drum 28. Mounted on the standard 31 is an electromagnet 40 which may be energized to move the disc 39 out of engagement with the surface 38 and into engagement with a similar surface 41 carried by the standard 31. The opposite end of the drum extension 36 is secured to a support 45.

Briefly, the driving unit operates as follows: Power, supplied by the motor, is transmitted through the worm 32, gear 33 and key 34 to the drum 28 and also through the clutch 38-39 to the shaft 29, thedrum 28 and shaft 29 are thereby caused to rotate at the same speed, When the drum and shaft have attained the desired rate of rotation, the electromagnet is energized to bring the disc 39 into engagement with the surface 41, whereby the shaft 29 is stopped and held stationary. Since the drum continues to rotate and is coupled by the nut 3'? to the stationary shaft 29, the 'drum, while continuing to rotate at the desired speed, will be caused to move longitudinally of the shaft.

Mounted on one end of shaft 29 is a disc 43 which carries a band 44 of the type shown in developed form in Fig. 5. This band extends completely around the disc 43 and is identical in the number of sections, relative lengths or" the respective sections, compared with the length of the band, and their sequential arrangement with the band shown on the face of disc 13.

- 'I'he'picture 2'7 to be transmitted is wrapped around and held fixedly on the drum 28 and light of constant intensity supplied by the source 25 is focused by an optical system, herein indicated by the lens 26, to provide a spot of light which illuminates successive elemental areas of the picture .as the drum moves relatively thereto. The picture 27 may be opaque for the purpose of reflecting light from its successive elementalareas to a light sensitive device 129, which is thereby activated to cause the production of image currents corresponding in amplitude to the tone values of the successive elemental areas oi the picture.

If desired, the picture maybe a transparency mounted on a transparent drum enclosing alight sensitive device, which is actuated by light passing through its successive elemental areas to cause the production of image currents of varying amplitudes. .In either case, the image currents are amplified by the device 4 .8 and transmitted over a communicating channel 49 to an amplifier 59 having in its output circuit a light source 51, which may be a glow lamp of the type disclosed'in an application of H. W. Weinhart, Serial No. 441,792, filed April 5, 1930 now Patent No. 1,918,309, dated July 18, 1933. Any other suitable source may be used, provided that it is adapted to supply light which varies with the changing amplitudes of the incoming image currents.

Light supplied by the source 51 is focused by an optical system, herein indicated by a lens 52, upon a recording surface carried by a drum 53. This drum is identical in design with the drum 28 at the transmitter and is adapted to be given a motion of rotation and translation by a motor (not shown), to which it is coupled through a driving unit similar in construction to the unit used to mechanically connect the drum 28 with the motor at the transmitter.

in accordance with standard practice, the drums 28 and 53 operate in phase and in synchronism with each other. This condition may be secured by properly adjusting the speed of one of the motors by a rheostat as disclosed in Fig. l, and the system therein shown may be used to indicate when the desired adjustment has been made.

The light sources 25 and 51 are enclosed in light proof casings 54 and 55, respectively, each provided with an aperture, through which light passes, and a handle whereby the casings may be adjusted to direct the light toward drums 28 and 53 during picture transmission periods, or toward the band 44 and mirror 56, respectively, during synchronizing periods.

During synchronizing periods the drums 28 and 53 are in the normal position at the extreme right, the casing 54 is adjusted to direct light to the band 44 and the casing 55 is adjusted to direct light to the mirror 56, as shown in Fig. 4. The drum 28 is driven at the desired rotary speed, with the clutch elements 38 and 39 in engagement, so that the drum does not move longitudinallyof the shaft 29. The beam of light supplied by source 25 through a lens system, if desired, illuminates successive elemental areas of the band 44. Light reflected from these elemental areas is applied to the light sensitive device 129 which is thereby activated to produce image currents varying in amplitude in accordance with the tone values of the successive elemental areas of the band. These image currents are transmitted over the picture channel 49 and are .supplied to the source 51. Light from the source 51 is directed by an optical system, herein indicated as consisting of mirror 56, lens 57 and mirror 58 to completely illuminate a disc 13 mounted on the shaft carrying the drum 53. Disc 13 is similar to that shown in Fig. 2 and carries on its face, directed toward the mirror 58, a circular band having black and white sectors identical in number, length and arrangement with those of band 44.

Drum 53 is brought up to speed, and light sup plied by source 51, which varies in accordance with the successive elemental areas of band 44 and hence in the same manner as the light passing through the sectors 5 to 12, inclusive, of disc 4, co-operates with the'black and white sections of disc 13 to produce a stroboscopic pattern having a single black line which becomes visible as the drums 28 and 53 approach synchronism. When synchronism has been attained the pattern will be stationary and by adjusting the phase of the motor driving drum 53 the black line may be caused to occupy a desired position which indicates that the two drums are in phase. The desired position may be identified by an indicator 59 carried by the standard 31.

With a picture mounted on drum 28 and a light sensitive record sheet applied to drum 53 and the drums adjusted to operate in synchronism and in phase, as described above, picture transmission is effected as follows: The casings 54 and 55 are set to direct a beam of light on the picture and record sheet, respectively. and the drums are given a motion of translation by simultaneously energizing the electromagn'ets 40 at the transmitting and receiving stations.

Application of a starting impulse simultaneously to the electromagnets 40 may be controlledby the transmitting or receiving operator over a circuit including a battery 60, relay 61, switch' 62, at the transmitter, one conductor of the transmission line 49, switch 63 and relay 64 to ground at the receiver. With switch 63 closed, the transmitting operator completes the control circuit by closing switch 62, or, if this operation is to be performed by the receiving operator the switch 62 will be closed and the control circuit will be completed by closing switch 63. Closure of either starting switch with the other closed will cause current to flow from one terminal of battery through upper winding of relay 61, switch 62, lower conductor of circuit 49, switch 63, upper winding of relay 64 and ground back to the other terminal of battery 60. Relays 61 and 64 will be energized to pull up their armatures 65 and 66 to complete the following circuits. .At the transmitter, current will flow from one terminal of battery 67, through switch 68, conductor 69, magnet 40, armature 65, lower or lock-up winding of relay 61 and through ground to the other terminal of battery 67. The electromagnet 40 at the receiver will'be energized by current flowing from one terminal of battery '70, switch 71, conductor 72, magnet 40, armature 66, lower or lock-up winding of relay 64 and through ground to the other terminal of battery 70. The magnets 40 are thereby simultaneously energized to cause disc 39 to engage surface 41 on the standards 31, at both stations, whereby the shafts 29 are stopped and held stationary. Since the drums 28- and 53 are rotating at the desired speed and are coupled by the nut 37 engaging the screw thread on the shaft 29, these drums will be caused to move longitudinally of the shaft 29, whereby successive elemental areas of the picture and of the light sensitive record sheet will be illuminated by light supplied by the respective sources 25 and 51.

Upon completion of the transmission of the picture, the energizing circuit for the magnets 40 may be opened by actuating switches 68and 70. These switches are placed in the path of the support 45, carried by the drums 28' and 53, whereby they are operated to open the circuit of the electromagnets 40. when ,the drums are in the extreme left-hand position on the shafts 29. The

drums may be returned to their normal position at "the extreme right, either by reversing, the motors or by disconnecting them from the drums and restoring the latter manually.

Fig. 6 shows one of the drums in the extreme left-hand position with the support 45 engaging switch 68 to open the circuit through which energizing current is supplied to the electromagnet 40.

Fig. 7- illustrates a receiving station with certain of the elements arranged in a manner different from that described in connection with Fig. 4, but which operates to effect the same result. A band 73, similar to that shown in Fig. 5, is mounted peripherally of the drum 53 to rotate therewith A source of light 74 completely surrounds the drum 53 and is adapted to be connected to the amplifier 50, in place of the source 51. With the drums rotating and a beam of light supplied to the band 44 at the transmitter, source 74 will supply light, varying in accordance with the tone -.'values of successive elemental areas of the band 44, which is reflected from the mirror 75 to completely illuminate the band '73 to produce a strob oscopic pattern.

Associated with the band '73 is a second mirror 76 completely surrounding the drum and so mounted that an observer may see the complete pattern and a reference mark positioned adjacent theband. When the drums are in synchronism, the pattern will appear as a stationary circular gray field with a bright section having a black line medially thereof. By adjusting the phase of the motor driving the drum 53, the position of the black line may be made to coincide with the reference mark which indicates thatplifler 50 is disconnectedfrom the source 74 and.

connected to the source 51, the casing 55 is adjusted to direct a beam of light on the light sensitive record sheet and transmission is effected in the manner described above in connection with Fig. 4. I

A slightly different arrangement for practicing the invention is shown in Fig. 8, in which the light source 51 is energized by incoming image currents, as in the system of Fig. 4, to illuminate successive elemental areas of a band 77 wrapped around the end of the drum 53. This band is similar to that described above and operates to reflect light which passes through an opening 78 At one point the illumination will be 5 nated has been'described, the invention is not limited to the use of this design, since many other arrangements of black and white sectors will give similar results. From an empirical study of a number of arrangements, it appears that the limiting case may be one in which the sectors under one point in the band used at the receiver are either all white or all black during the intervals of illumination, while the sectors under the remaining points are half black and half white.

The stroboscopic arrangement described herein is applicable to any installation including a rotating machine which must be operated in phase and at synchronous speed. When used in electro-optical systems, it possesses the further advantage that the pattern on the band at the sending end can be used as a standard of transmission which will permit the sending and receiving apparatus to be adjusted-for picture or image transmission. On the basis of the theory relating to the transmission of pictures and images, as now practiced, it is necessary to introduce a considerable bias into the original signal. This bias will have the effect of increasing the direct current component of the original signal beyond the value determined by the picture or object itself, and conse quently it must be removed at the receiver.

The routine of adjusting the receiver will involve setting the gain so that the variations cover the proper range and then setting the local bias so that the variations occur between the proper absolute limits. The two adjustments correspond, in effect, to adjusting both the alternating current and direct current components of the current delivered to the receiving light source. During the synchronizing period the operator at the transmitter will adjust the sending apparatus so that currents of the proper amplitude for picture transmission are sent over the line, and at the co-operating station, the operator can then adjust the receiving apparatus for picture or image reception. This may be accomplished without communicating with the transmitting operator, thereby avoiding delay and hence simplifying the operation of the system.

The light source 51 at the receiving station may be replaced by a suitable light value, as disclosed, for example, in U. S. Patent 1,667,805, May 1, 1928 of H. E. Ives.

What is claimed is:

1. stroboscopic apparatus comprising means for producing light flashes recurring at irregular intervals during a given period of time, a rotatable element having alternate light reflecting and absorbing segments circularly arranged to constitute a set about the center of rotation, some of said reflecting segments having angular dimensions difierent from others, and means for applying light from said flashes to said rotatable element. 1 a

2. stroboscopic apparatus comprising means for producing light flashes recurring at irregular intervals during a given period of time, a rotatable disc having alternate light reflecting and absorbing segments circularly arranged to constitute a set about the center of rotation, some of said reflecting segments having angular dimensions different from others, and means for applying light from said flashes to said rotatable element.

3. A stroboscopic apparatus comprising means for producing light flashes recurring at irregular intervals during a given period of time, a rotatable element having alternate segments responding differently to light incident thereon and circularly arranged to constitute a set about the center of rotation, some of said segments having angular dimensions difierent from others, and

means for applying light from said flashes to said rotatable element.

4. A stroboscopic apparatus comprising means for producing light flashes recurring at irregular,

intervals during a given period of time, a rotatable element having alternate segments responding differently to'light incident thereon and circularly arranged to constitute a set about the center of rotation, the alternate segments constituting separate groups comprising segments some of which have dimensions different from others, and means for applying light from said flashes to said rotatable element.

5. A stroboscopic apparatus including means for producing light flashes recurring at irregular intervals during a given period of time, a rotating element carrying a circularly arranged pattern comprising segments of increasing and decreasing lengths and separation respectively over at least -aportion of the pattern, and means for applying light from said flashes to said rotatable element.

6. A stroboscopic apparatus comprising means for producing light flashes recurring at irregular intervals during a given period of time, a rotating element carrying a circularly arranged pattern comprising segments of increasing lengths and separation over at least a portion of the pattern, and means for applying light from said flashes to said rotatable element.

7. A stroboscopic apparatus comprising means for producing light flashes recurring at irregular intervals during a given period of time, a rotating element carrying a circularly arranged pattern, comprising segments of decreasing lengths and separation over at least a portion of the pattern, and means for applying light from said flashes to said rotatable element.

8. A stroboscopic apparatus comprising a mov ing member for controlling the generation of a plurality of irregularly occurring radiant energy impulses during each cycle thereof, a second member provided with a series of spaced elements on which said radiant energy impulses are incident, and means for moving said last mentioned member to carry said elements-over a path common thereto to modify the efiect of said radiant energy and thereby indicate the relative speed of movement of said members.

9. A stroboscopic apparatus comprising a moving member for cyclically controlling the generation of a plurality of radiant energy impulses of irregular occurrence and duration within the cyclic period, a second member provided with a series of spaced elements having lengths proportional to the duration of the recurrent radiant energy impulses respectively and on which said impulses are incident, means for moving said elements on which saidgradiant energy impulses are incident, and means for moving said last mentioned member to carry said elements over the same path to modify the efiect of said radiant energy and thereby indicate the relative speed or movement of said members.

11. A stroboscopic apparatus comprising a source of radiant energy, a movable member having a series of radiant energy modulating elements for receiving radiant energy from said source, means for moving said member to cause said elements to traverse a unitary path supplied with radiant energy Irom said source, a second movable member provided with elements for controlling by their movement the radiant energy from said source to cause the production of a definite series of impulses in part at least of different duration and differently spaced in time, and means for moving said second member to cause said impulses to occur in correspondence with the traversal of said energy modulating elements in said path.

12. An apparatus comprising a source of radiant energy, a movable member having a series 01' radiant energy modulating elements for receiving radiant energy from said source, means for moving said member to cause said elements to traverse a path supplied with radiant energy from said source, a second movable member having means for controlling the energy from said source to cause the emission of a definite series of impulses in part at least of different duration and differently spaced in time, and means for moving said second member to cause said impulses to occur with spacing and duration corresponding to the spacial distribution and extent of said energy modulating elements in said path.

JOSEPH W. HORTON. 

